1. Field of the Invention
The present invention relates to a combustion chamber for a gas turbine and, more particularly, to impact cooling a combustion chamber with a multi-walled construction.
2. Description of Related Art
One of the most demanding thermal environments in a gas turbine is the combustion chamber where fuel is burned. The extremely high temperatures achieved in the combustion chamber require special measures for cooling the chamber walls.
U.S. Pat. No. 5,083,422 describes a aircraft engine gas turbine having a combustion chamber with a combustion zone including an internal space for guiding the hot combustion gases. The internal space at its upstream end directly adjacent to a burner is surrounded by an inner wall. In that vicinity the inner wall is of a non-perforated configuration, that is, impermeable to air and is surrounded by a casing with three rows of holes for the inflow of cooling fluid. Most of the compressed air from a compressor goes to the burner, but a small part is introduced to a side of the inner wall facing away from the internal space, where some of the air passes through the holes in the casing to form a plurality of cooling-air jets that impinge on the inner wall. The cooling air entering through the holes in the casing is then guided directly into the internal space, where the now-heated cooling air mixes with the combustion gases.
U.S. Pat. No. 4,550,562 discloses using steam to cool gas turbine parts. The combustion chamber has combined air and steam cooling using an open-air cooling circuit in which cooling air flows around the combustion chamber and is supplied to the hot gases flowing within the latter. Cooling steam is conducted in a closed circuit through pipes disposed around the combustion chamber to form its inner wall.
U.S. Pat. No. 4,819,438 discloses a gas turbine combustion chamber with convective cooling using steam. The combustion chamber has a wall enclosing an internal space that guides the hot combustion gases. The wall structure includes an inner wall exposed to the hot gases and an outer wall that forms a space between the outer and inner walls. The space has an inlet and an outlet for cooling steam, and formed therein are spiral paths through which cooling steam flowing into the space is guided.
However, those skilled in the art still seek a better system for cooling gas turbine combustion chambers.
It is an object of the present invention to avoid the shortcomings of prior art structure for cooling gas turbine combustion chambers, and particularly to provide a multi-walled combustion chamber with impact cooling.
It is another object of the present invention to provide a combustion chamber having a wall structure capable of being cooled by cooling steam, as well as a method for steam cooling such a combustion chamber.
In furtherance of the objects of the present invention, one aspect of the invention involves a combustion chamber comprising a wall structure having an outer wall for mechanically supporting the combustion chamber and an inner wall forming an internal space through which combustion gases flow from a chamber inlet to a chamber outlet, the inner wall and the outer wall defining an envelope therebetween, an intermediate wall disposed in the envelope and defining an inner cooling space between the inner wall and the intermediate wall and an outer cooling space between the intermediate wall and the outer wall, and a cooling fluid inlet in the outer space and a cooling fluid outlet in the inner space, wherein the intermediate wall has a plurality of orifices for permitting the flow of cooling fluid therethrough for impact cooling the inner wall.
A more specific aspect of the invention involves such a combustion chamber wherein the outer cooling space has an outer cooling space cross-sectional flow area that is variable along a direction of flow of cooling fluid, the outer cooling space cross-sectional flow area being in a substantially constant first ratio to the sum the areas of all of the orifices downstream of a given outer cooling space cross-sectional location, and the inner cooling space has an inner cooling space cross-sectional flow area that is variable along a direction of flow of cooling fluid, the inner cooling space cross-sectional area being in a substantially constant second ratio to the sum the areas of all of the orifices upstream of a given inner cooling space cross-sectional location, and the first and second ratios are substantially the same.
Another aspect of the invention relates to a method for steam cooling a combustion chamber having an inner wall for exposure on one side thereof to combustion gases, the method comprising the steps of providing an intermediate wall between the inner wall and an outer wall, the intermediate wall having therein a plurality of orifices, and passing cooling steam through the orifices and impacting the steam against another side of inner wall facing away from the combustion gases.